forked from Minki/linux
44348e8ac1
As files move around, their previous links break. Fix the references for them. Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com> Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Acked-by: Jonathan Corbet <corbet@lwn.net>
68 lines
2.9 KiB
Plaintext
68 lines
2.9 KiB
Plaintext
Chinese translated version of Documentation/io_ordering.txt
|
||
|
||
If you have any comment or update to the content, please contact the
|
||
original document maintainer directly. However, if you have a problem
|
||
communicating in English you can also ask the Chinese maintainer for
|
||
help. Contact the Chinese maintainer if this translation is outdated
|
||
or if there is a problem with the translation.
|
||
|
||
Chinese maintainer: Lin Yongting <linyongting@gmail.com>
|
||
---------------------------------------------------------------------
|
||
Documentation/io_ordering.txt 的中文翻译
|
||
|
||
如果想评论或更新本文的内容，请直接联系原文档的维护者。如果你使用英文
|
||
交流有困难的话，也可以向中文版维护者求助。如果本翻译更新不及时或者翻
|
||
译存在问题，请联系中文版维护者。
|
||
|
||
中文版维护者： 林永听 Lin Yongting <linyongting@gmail.com>
|
||
中文版翻译者： 林永听 Lin Yongting <linyongting@gmail.com>
|
||
中文版校译者： 林永听 Lin Yongting <linyongting@gmail.com>
|
||
|
||
|
||
以下为正文
|
||
---------------------------------------------------------------------
|
||
|
||
在某些平台上，所谓的内存映射I/O是弱顺序。在这些平台上，驱动开发者有责任
|
||
保证I/O内存映射地址的写操作按程序图意的顺序达到设备。通常读取一个“安全”
|
||
设备寄存器或桥寄存器，触发IO芯片清刷未处理的写操作到达设备后才处理读操作，
|
||
而达到保证目的。驱动程序通常在spinlock保护的临界区退出之前使用这种技术。
|
||
这也可以保证后面的写操作只在前面的写操作之后到达设备（这非常类似于内存
|
||
屏障操作，mb()，不过仅适用于I/O）。
|
||
|
||
假设一个设备驱动程的具体例子：
|
||
|
||
...
|
||
CPU A: spin_lock_irqsave(&dev_lock, flags)
|
||
CPU A: val = readl(my_status);
|
||
CPU A: ...
|
||
CPU A: writel(newval, ring_ptr);
|
||
CPU A: spin_unlock_irqrestore(&dev_lock, flags)
|
||
...
|
||
CPU B: spin_lock_irqsave(&dev_lock, flags)
|
||
CPU B: val = readl(my_status);
|
||
CPU B: ...
|
||
CPU B: writel(newval2, ring_ptr);
|
||
CPU B: spin_unlock_irqrestore(&dev_lock, flags)
|
||
...
|
||
|
||
上述例子中，设备可能会先接收到newval2的值，然后接收到newval的值，问题就
|
||
发生了。不过很容易通过下面方法来修复：
|
||
|
||
...
|
||
CPU A: spin_lock_irqsave(&dev_lock, flags)
|
||
CPU A: val = readl(my_status);
|
||
CPU A: ...
|
||
CPU A: writel(newval, ring_ptr);
|
||
CPU A: (void)readl(safe_register); /* 配置寄存器？*/
|
||
CPU A: spin_unlock_irqrestore(&dev_lock, flags)
|
||
...
|
||
CPU B: spin_lock_irqsave(&dev_lock, flags)
|
||
CPU B: val = readl(my_status);
|
||
CPU B: ...
|
||
CPU B: writel(newval2, ring_ptr);
|
||
CPU B: (void)readl(safe_register); /* 配置寄存器？*/
|
||
CPU B: spin_unlock_irqrestore(&dev_lock, flags)
|
||
|
||
在解决方案中，读取safe_register寄存器，触发IO芯片清刷未处理的写操作，
|
||
再处理后面的读操作，防止引发数据不一致问题。
|